Abstract
Abstract We report on a new multifocus optical system developed for fluorescence correlation spectroscopy (FCS). This system utilizes a beamsplitter array to spatially separate excitation beams. Fluorescence from each spot is individually detected with a single-photon avalanche photodiode (SPAD) through a fiber bundle. The combined use of beamsplitters and multiple SPADs is beneficial to give a higher detection uniformity among focal spots than the existing multifocus FCS systems. Applications of this setup show that the variation of the optical parameters among seven focal spots are as small as ∼5% and prove its high performance in FCS measurements. High efficiency of this system is also demonstrated in application to an advanced FCS method, two-dimensional fluorescence lifetime correlation spectroscopy. Along with the results of these applications, we describe a method for proper correction of the crosstalk effect in the multifocus setup.
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